The proposed Phase II research focuses upon an application specific integrated circuit (ASIC) that is necessary to support new avalanche photodiode (APD) and lutetium orthosilicate (LSO) detector module designed for small-animal PET applications. Based on our Phase I experience, advanced research and development will be carried out to design and fabricate a sophisticated 64-channel ASIC readout for RMD APD arrays. The new design will encompass all of the Phase I prototype's desirable properties while correcting its defects. Subsequent research will be carried out to enable the coupling of the ASIC directly to the APD array. The resulting module will be thoroughly tested and evaluated. This work will directly enable and facilitate the use of compact APD arrays in small animal PET (and imaging systems in general) by providing a high-density readout scheme capable of processing the large number of signals produced by the array. The high-performance readout ASIC will replace old, bulky, modularized equipment, increase the performance of entire PET systems, and decrease the cost to implement these systems. We envision an LSO/APD/ASIC module that will form the basis of a commercial product to be primarily produced and assembled by RMD that will principally be used in high-resolution, small-animal PET. The adaptation of the module to clinical and human PET will comprise future Phase Ill commercialization work.